Optical multiplexing and switching devices are used for high speed data communications over long distances. Standards, such as ITU-T G.709 and IEEE 802.3 100 G Ethernet, enable communications of large volumes of data. ITU-T defines an Optical Transport Network (OTN) as a set of Optical Network Elements (ONE) connected by optical fiber links, able to provide functionality of transport, multiplexing, switching, management, supervision and survivability of optical channels carrying client data. The client data can be generated from Gigabit or higher rate Ethernet cards and mapped to OTN signals before transmission, or several low order Optical channel Data Unit (ODU) which are multiplexed to a high order ODU before transmission. The signals are received and processed by device nodes. The processing can in multiplexing, de-multiplexing, and switching operations.
As shown in FIG. 1, an Optical channel Data Unit (ODU) switch node 100 can include client cards 110, line cards 120, and a switch card 130. Other variations of the ODU switch 150, as shown in FIG. 2, only have line cards. However, the underlying operational principles are similar, i.e., inputting ODU signals, switching, multiplexing/de-multiplexing the signals, and then outputting the ODU signals. Conventionally, only one switch card or a Clos network of multiple switch cards is used, e.g., see U.S. Pat. No. 4,967,405. All data passes through the single switch card. Hence, the switch card can be a single point of failure. Therefore, it is desired to increase the reliability of the ODU switch.
One way to increase reliability is with optical link redundancy; this is called 1+1 protection, which can increase costs and network overhead.
Redundant switches are also known. A simple architecture uses primary and standby switch cards. All data are normally switched by the primary card. If a, usually centralized, monitoring or control mechanism detects a failure, then the standby switch card is activated. This is called 1:1 switch protection. A more sophisticated architecture has N+K switch cards. N switch cards are normally functional at any given time, and K switch cards are in standby mode. If one of the N cards fails, then one of the K standby cards is activated. Any delays in detecting a failure and switching to the standby card can result in a loss of a significant amount of data.
Redundancy has also been used for increased throughput and load balancing. In this architecture, the data are distributed, over multiple parallel switch cards that run in parallel. However, parallel cards do not necessarily increase reliability. In fact, the probability of card failures is increased to decrease reliability.